WASHINGTON — Continuing problems with an Exelis-built payload will delay the delivery of the first of the GPS 3 next-generation navigation satellites, a senior U.S. Air Force official said Feb. 7.

Gen. William Shelton, commander of Air Force Space Command, said the issue highlights the problem inherent in relying on one contractor for a critical technology. Exelis Geospatial Systems of Rochester, N.Y., has supplied the payloads for all previous generations of GPS satellites.

The latest payload delay is not expected to push back the first launch of the Lockheed Martin-built GPS 3 satellites at this point. Nonetheless, Shelton made clear his patience is wearing thin.

“Both the prime and the sub know exactly where we stand on this,” Shelton said in remarks at a Capitol Hill Club breakfast.

Lockheed Martin Space Systems of Denver is under contract to build eight GPS 3 satellites, the first of which is slated to launch in 2015. The satellites are expected to be more accurate and reliable than previous generations of GPS craft.

In December 2012, Exelis announced it had integrated and performed initial testing of a payload aboard a prototype GPS 3 satellite. But the company has struggled with the navigation payload since at least this past September, when Shelton mentioned the problem publicly.

In November, Exelis officials said they believed “the known technical issues have been resolved” and that the payload was expected to be delivered in spring 2014. At the time, they said the delays stemmed from “first-time development and integration issues, including design changes to eliminate signal crosstalk.” Crosstalk occurs when a signal broadcast on one circuit creates an undesired effect on another circuit.

Chip Eschenfelder, a Lockheed Martin spokesman, said via email Feb. 7 that while “known performance issues have been resolved, we test thoroughly across the full range of launch and space flight mission environments to ensure that there are no residual problems.”

That testing is ongoing, Eschenfelder said. “Lockheed Martin and Exelis are doing whatever it takes to get this first navigation payload right,” he said.

Shelton said he expected the current problems would push the delivery of the satellite from late 2014 into 2015, but most likely would not postpone the initial launch.

Shelton was visibly frustrated with the issue and suggested that the U.S. government might benefit from having a diversity of GPS payload providers.

“There is exactly one provider for navigation payloads,” Shelton said. Although not ready to abandon Exelis, Shelton said he has encouraged industry to work on an alternative payload.

The Air Force has tried in the past — with mixed results — to create competition where none previously existed.

Exelis spokeswoman Jane Khodos said in a Feb. 7 email that GPS 3 will meet all mission and quality requirements.

“We want to make sure to get everything right before the payload goes into space, especially with this first one,” Khodos said. “Significant testing with flight-like engineering units and the first GPS III satellite’s flight hardware indicates that the known technical issues have been resolved.”

Meanwhile, Shelton also raised questions about the long-term viability of the existing GPS constellation, calling some of the on-orbit satellites “fragile.”

“We’re a little bit concerned about the long-term viability of the satellites,” he said, joking that some of the satellites were old enough to vote.

Currently, 31 GPS satellites are on orbit, including eight from the legacy Block 2A program. The first of those satellites, which were designed for a 7.5 year lifespan, were launched in 1990.